Simon Fox has expressed concern at the decline of the UK high street. Photograph: Frank Baron for the Guardian

HMV's chief executive Simon Fox hit out at the relentless growth of the UK supermarket industry on Friday, after reporting another slump in sales, but said the firm's focus on festivals and accessories was cause for optimism.

"There are millions of feet of new supermarket space being built over the next few years. How will that affect the high street?" Fox asked. He also pointed to the threat posed by new shopping centres – such as the new Westfield site in Stratford, where HMV is opening a new store, while shutting its nearby high street outlet.

Fox was speaking after HMV reported a like-for-like sales slump of 15% over the past 18 weeks, in line with City forecasts. The company has, however, seen a 100% increase in sales of technology products, such as iPads and speaker docs, at its new Fast Forward stores. It is now rolling the format out across most of its estate this month.

"I'm more optimistic than when we last updated you in May," Fox said. HMV Live runs festivals including High Voltage and Global Gathering, Lovebox, and it saw attendances rise by 30% this summer.

City analysts believe HMV will have to launch a rights issue to strengthen its capital base. Fox said an equity fundraising was "not on the table today", and could not be considered until HMV had shown that its business was improving.

Fox told reporters that the company had been "massively distracted" over the past six months, but was now fully focused on the crucial Christmas trading period.

HMV has closed 29 stores over the past 18 weeks, as it focuses on its more profitable sites. It is also setting up new sites, as well as the HMV Ritz, its new 1500-capacity venue in Manchester, which opened on Tuesday."It's not all doom and gloom," Fox insisted. "Our customers will be there for Christmas."

Freddie George, analyst at Seymour Pierce, said HMV's sales remained "very weak", and kept his sell recommendation on the firm.

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